This invention relates to apparatus for fabricating wood structures, and is more particularly concerned with apparatus for fabricating shallow depth flat trusses for use as floor joists or the like.
More particularly, this invention is an improvement in apparatus for fabricating wood structures, such as disclosed in my U.S. Pat. No. 3,866,530. The apparatus disclosed in my above-mentioned patent effectively overcame many of the problems encountered in the fabrication of shallow depth flat floor trusses. More particularly, this apparatus enabled the fabrication of a wide variety of sizes and configurations of flat floor trusses at high production rates.
Specifically, this above-mentioned apparatus utilized an elongate frame which carried a plurality of supports movable longitudinally along the frame in back-to-back relation for supporting the wood members in position for being secured together by the nailing plates. However, upon forcibly biasing or jigging the wood members in abutting relationship with one another prior to being secured together by nailing plates, a substantial outward clamping load was exerted on the support members which tended to cause the support members on opposite sides of the frame to open up from their intended back-to-back relation. This opening up of the support members caused mislocation of the wood members and induced unwanted inaccuracies in the truss.
This prior apparatus utilized two presses, one for each side of the frame, each of which was mounted on a cart movable along the frame. Each cart had a control system for accurately stopping the cart at an operating position at each support and for initiating operation of the press to drive nailing plates into the wood members at each support. Movement of the press mounting cart was controlled by proximity switches carried by the press cart actuable by means, such as a magnet, mounted on the frame at each desired operating position. However, as the cart moved laterally along the frame, the press tended to move in and out relative to the frame. Under certain circumstances the proximity switches were not tripped at the desired time thus preventing operation of the press at an intended location.
The above-described prior art apparatus also utilized an automatic ejector system for removal of completed trusses from the apparatus. It was found, however, in some cases that after fabrication the ends of the truss would sometimes become wedged between various wood member clamps thus making ejection of a completed truss difficult. More particularly, it was found that if the truss ejectors at the center of the truss were actuated prior to the ejectors at the ends of the truss, the center of the truss would be bent up thus causing the length of the truss to increase.